This invention relates to a gain and equalization system and more particularly to a digital gain and equalization system for reducing distortion, phase shift and other anomalies, and improving "clarity" in a variety of currently available sound systems.
Sound generation, recording and reproduction systems may take a variety of forms and perform a variety of functions, all relating, of course, to processing sound signals, with the common objective being to ultimately reproduce as accurately as possible the sound originally created or recorded or even "enhance" it. Such systems include, among others, public address systems and similar systems which utilize microphones and speakers, radio and television broadcast systems, radio and television receivers, tape recorders and disk recorders and players, home, auto and portable stereo systems, and recording studio systems. In all such systems, the sound is converted to electrical audio signals representing the sound, processed in some way, and then either reproduced, transmitted to other locations or recorded. At the various stages of generating the sound and processing the audio signals, there is a chance that either noise will be introduced to mask the true signals or the signals will be distorted (undesired change in signal waveform) in such a way that it is difficult to accurately reproduce the sound. Such noise and/or distortion may arise in the sound source itself, for example, instruments, voices, etc., in the room or studio acoustic configuration, in microphones which pick up the sound and convert it to electrical audio signals, in audio amplifiers and other audio signal processing components, in recording equipment and recording media, in speaker systems, and in audio signal transmitting equipment.
Ideally, all noise would be removed from (or not allowed to initially influence) the audio signal, and all processing of the audio signal would take place free from distortion, e.g., amplification would occur equally and uniformly over the entire audio signal frequency band (audio spectrum). However, achieving an essentially undistorted resultant audio signal has not been possible; rather in the course of reproducing an audio signal and otherwise processing such a signal, distortion of some form (phase distortion, frequency distortion, harmonic distortion, intermodulation distortion and the addition of noise) is inevitably introduced.
Distortion, which is frequency dependent, means that the signal being processed is treated differently, e.g. amplified or phase shifted by different amounts, at the different frequencies contained in the signal. Such distortion prevents the accurate reproduction of the original sound transmitted, recorded, or produced.
In an attempt to reduce, to the extent possible, distortion and other undesirable deficiencies produced by room acoustics, microphones, loudspeakers, recorders, and other audio signal producing and processing components, what are called "equalizers" are provided. Equalizers effect or introduce a kind of controlled distortion of the frequency response which is ideally flat, for the purpose of offsetting or cancelling the distortion introduced during signal origination production and processing. Equalizers, in effect, alter the frequency response of an audio system in some desired manner. Initially equalizers were constructed of passive components, to provide attenuation or cuts at certain frequencies. Later designs were usually constructed with active components, typically vacuum tube circuits and operational amplifiers.
Among the more well known equalizers in use today is the so-called graphic equalizer which is incorporated into many professional, home and automobile sound systems. The graphic equalizer is generally constructed so that the console and controls present the appearance of a graphic display of the frequency response being developed by the equalizer, e.g., which bands of the audio signal are boosted and which are cut.
In another type of equalizer, known as the parametric equalizer, three parameters of equalization, including frequency selection, boost or cut, and bandwidth control, are all independently variable.
More elaborate studio equalizers are utilized in recording, broadcast and television studios and these consist basically of a parallel bank of band-pass filters in which the center frequencies of the filters are separated by some finite amount such as an octave or fraction thereof, typically one-third. The gain or attenuation of each filter is separately adjustable, the result of which is an overall frequency response which can be continuously set across the entire audio frequency range.
In spite of the various approaches to performing "equalization", performing it in a high quality fashion, with little phase shift, and in a simple and inexpensive manner has been difficult to achieve.